Yes, I think the end user is in a better position than Google to decide who to trust. Some end users will make bad decisions, but Google's interests are systematically misaligned with theirs.

Not really. Google has maybe the best security researchers in the world, most end users have no idea, Hacker News is not representative of the general population.

I am not saying it justifies locking down devices, but that's the kind of situation where I think a bit of friction is a good thing. For example having to connect your phone to a computer and run some command line tool (like for unlocking a bootloader). You still have your freedom, but it is also something you are less likely to do by accident. In the sideloading situation, it looks like you could make yourself a developer account and repack apps under your own identity, which is one of these high friction workarounds.

For F-Droid specifically, maybe they should negotiate with Google before going to the offensive. Maybe they did and it didn't work, but I think a good compromise would be to let F-Droid has a key to sign the apps they compile, making F-Droid accountable for the apps they distribute.

And by the way, Firefox is in a similar situation for extensions. Over the years, they made it really hard to install anything from outside the official Mozilla repository, citing security concerns. It is not just Google.